In most industrial air conditioning systems it is required that the air in the treated space be maintained at prescribed temperature and humidity levels. Toward this end air is taken from a treated area, which air has increased in temperature (temperature rise) due to the heat of the machines in the area, the number of people in the area, the type of processing being carried out in the area, and even the outside weather conditions. This return air is passed through a conditioning system where it is cleaned, cooled, and the humidity thereof controlled to such an extent that the room conditions including the humidity level may be maintained. It is imperative in many, particularly industrial, situations that the absolute humidity level be maintained constant so as not to adversely effect the processing carried on therein.
In conventional air conditioning equipment such goals have been accomplished by completely cooling the return air in an air washer to substantially the dew point corresponding to the absolute humidity level of the treated space. Such an approach is quite satisfactory assuming the temperature difference between the dew point and room conditions equals the actual temperature rise which occurs. However, for various reasons such full load temperature rise does not occur. For example, on a cloudy or cool day, or where some machines are idle or for other similar reasons, the full load conditions do not exist and in fact the temperature rise may only be 50% to 70% of the temperature difference between dew point and room conditions. If full load treatment continues, the temperature will drop below the desired level.
In known systems such partial load conditions are compensated for in one of two ways or a combination of the two. First of all the supply air may be heated by an auxiliary heating device immediately upon its leaving the air washer and prior to the time it is introduced into the heated space to such an extent that, when coupled with the room conditions, the full load temperature rise will occur. Secondly, some of the return air may be routed around or by-pass the air washer so that not all of the return air is treated. Also, combinations of these two systems are commonly utilized. Both solutions to the problem, however, have undesirable characteristics. For example, intentional heating of the supply air requires wasted energy input, as well as requiring the chilling of the return air past the desired temperature point all the way back to the dew point; it being understood that the only way to control a system in which a dry bulb thermostat can satisfactorily control the system is to first of all achieve saturation. In the second approach (by-pass) additional space and equipment is required to route a portion of the air around the washer which results in more expensive and space consuming installations.
The real problem of the above systems which has been realized and overcome in the instant invention is the conventional use of the dry bulb temperature sensing device to control the moisture content. A dry bulb temperature sensing device has no way of measuring and maintaining a desired humidity level in the air. Therefore in such systems the only way to be sure of maintaining a desired moisture content, as well as a prescribed temperature is to cool all the way to the dew point (saturation), then reheat or by-pass as discussed above.